1. Field
Disclosed herein is a laminate stack comprising individual soft magnetic sheets, an electromagnetic actuator for controlling a quantity of fuel to be fed into an internal combustion engine for example, and a process for their manufacture.
2. Description of Related Art
An electromagnetic actuator comprises a valve seat with a fitting valve body, it being possible to move the valve body by means of a magnetic field acting on a magnet armature connected to the valve body. In this arrangement the magnetic field is built up by passing a current through a coil, the magnetic flux penetrating the magnet armature with a time delay.
Short switching times of less than 40 μs to 100 μs are desirable, particularly in electromagnetic actuators used as injection valves. In order to achieve short valve switching times, the time delay between the passing of the current through the coil and the build up of the magnetic field in the magnet armature should be as short as possible. An important factor limiting the lower end of the time delay range is the occurrence of eddy currents induced in the electrically conductive bodies of the magnet armature by the time change in the magnetic field.
An injection valve in which eddy currents generated in pole bodies between neighbouring coils cancel one another out by alternately passing current through said coils is described in DE 100 05 182 A1. The disadvantages of this arrangement are that this cancelling out of eddy currents can only be achieved locally and that the magnetic flux is also cancelled out. However, losses due to eddy currents remain high and prevent fast switching times. In addition, the constraints placed on the geometry of the coils and pole bodies in achieving maximum cancelling out of the eddy currents severely limit the design of the injection valve.
A further approach to reducing eddy currents is described in DE 103 19 285 B3 which discloses an injection valve which has radially running slits in both the magnet armature and the magnet core, it being possible for the magnet core to be made of stacked, slit iron sheets or alternatively of iron rings stacked concentrically one inside the other or in the manner of a toroidal core.
However, this injection valve has several disadvantages. Almost no magnetic flux passes through the slit-shaped air gaps and the conductor surface through which the magnetic flux passes is therefore lost and the valve is able to withstand only short opening and closing forces. In such arrangements, moreover, the flux is required to flow parallel to the sheet normal and radially in relation to the concentric rings, respectively, and to pass across a gap between two sheets or rings, producing undesirably low permeability values for the system as a whole. This would have to be compensated for by a significant increase in the coil current which would, however, simultaneously promote eddy currents in the sheet levels.
Spirally or involutely layered laminate stacks for reducing eddy currents are described in publications JP 2002 343626 AA and DE 103 94 029 T5.
A fuel injection valve for fuel injection systems in internal combustion engines with a soft magnetic magnet yoke arrangement is described in DE 10 2004 032 229 B3. The arrangement has a first yoke sheet and a second yoke sheet which are rolled together in a spiral.
DE 35 00 530 A1 proposes an electromagnetically operated control system to control a lift valve in an internal combustion engine in place of a mechanical cam control system.